The present invention relates to antennas of geo-stationary satellites and, in particular, it concerns stabilizing two antennas mounted on a single pedestal.
By way of introduction, various geo-stationary satellites are located at approximately 36,000 Km from the surface of the earth around the equator in a belt known as the “Clark Belt”. These satellites serve satellite TV channels and two way communication such as internet, data video conferencing and voice communications. However, not all the TV channels are available from the communication satellites. For example, in the U.S.A. the communication satellites (FSS) which are located at 91 degrees West, 99 Degrees West and 116.8 degrees West do not include the Broadcast TV channels which are provided by the BSS satellites at 101 degrees West, 110 degrees West and 119 degrees West. Typically, on a mobile platform, for example, but not limited to a marine, airborne or ground mobile platform, there is a need to provide both two way communication and to receive broadcast TV channels. Therefore, there is a need to mount two antennas on the mobile platform in order to provide simultaneous links with two satellites, one for TV Receive Only communications (TVRO) and the other for two way (Tx/Rx) communication.
The simple and common solution is to use two separate pedestal/tracking antenna systems. This solution requires a large amount of space, is not cost effective and there may be interference between the two antennas if they are placed to close together. In addition, two radomes or one large radome are required which takes up additional space and is very expensive.
It is known in the field of antenna alignment to use a single antenna with multiple feeds, such that the antenna receives signals from a plurality of satellites. However, the Regulatory authorities, such as the FCC and ETSI require that the end-user terminal be aligned very accurately with a satellite in order for the end-user to transmit to the satellite. The alignment accuracy required by the Regulatory authorities cannot be achieved using a multiple feed system.
It is also known in the field of antenna alignment systems to mount two antennas on a single pedestal for tracking low earth orbit (LEO) satellites. An example of such a system is taught by U.S. Pat. No. 6,310,582 to Uetake, et al. The aforementioned system is suitable for LEO satellites, but is not suitable for tracking two geo-stationary satellites.
There is therefore a need for a cost and space effective stabilization system for two antennas associated with geo-stationary satellites where at least one of the antennas is linearly polarized.